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A pandemic is a global disease outbreak. A flu pandemic occurs when a new influenza
virus emerges for which people have little or no immunity, and for which there is no
vaccine. The disease spreads easily person-to-person, causes serious illness, and can
sweep across the country and around the world in very short time.

It is difficult to predict when the next influenza pandemic will occur or how severe it will
be. Wherever and whenever a pandemic starts, everyone around the world is at risk.
Countries might, through measures such as border closures and travel restrictions, delay arrival of the virus, but cannot stop it.

A pandemic may come and go in waves, each of which can last for six to eight weeks.
An especially severe influenza pandemic could lead to high levels of illness, death, social
disruption, and economic loss. Everyday life would be disrupted because so many people in so many places become seriously ill at the same time. Impacts can range from school and business closings to the interruption of basic services such as public transportation and food delivery.

A substantial percentage of the world's population will require some form of medical
care. Health care facilities can be overwhelmed, creating a shortage of hospital staff,
beds, ventilators and other supplies. Surge capacity at non-traditional sites such as
schools may need to be created to cope with demand.

The need for vaccine is likely to outstrip supply and the supply of antiviral drugs is also
likely to be inadequate early in a pandemic. Difficult decisions will need to be made
regarding who gets antiviral drugs and vaccines.

Death rates are determined by four factors: the number of people who become infected,
the virulence of the virus, the underlying characteristics and vulnerability of affected
populations and the availability and effectiveness of preventive measures.

PANDEMIC DEATH TOLL SINCE 1900
(This as per the CDC)

1918 - 1919 US-675,000 Worldwide - 50,000,000+

1957 - 1958 US-70,000+ Worldwide - 1-2,000,000+

1968 - 1969 US-34,000 Worldwide - 700,000+


How are we preparing?

The United States has been working closely with other countries and the World Health
Organization (WHO) to strengthen systems to detect outbreaks of influenza that might
cause a pandemic.The effects of a pandemic can be lessened if preparations are made
ahead of time. Planning and preparation information and checklists are being prepared for various sectors of society, including information for individuals and families.

HHS and other federal agencies are providing funding, advice, and other support to your
state to assist with pandemic planning and preparation. Information on state/federal
planning and cooperation, including links to state pandemic plans, is available on this
site. www.cdc.gov/flu/Pandemic

The federal government will provide up-to-date information and guidance to the public
through the public media and this web site should an influenza pandemic unfold.
The 2008 recommendations include four principal changes or updates:

· Beginning with the 2008-09 influenza season, annual vaccination of all children
aged 5-18 years is recommended. Annual vaccination of all children aged 5-18
years should begin in September or as soon as vaccine is available for the 2008-09
influenza season, if feasible, but annual vaccination of all children aged 5-18
years should begin no later than during the 2009-10 influenza season.

· Annual vaccination of all children aged 6 months-4 years (59 months) and older
children with conditions that place them at increased risk for complications from
influenza should continue. Children and adolescents at high risk for influenza
complications should continue to be a focus of vaccination efforts as providers
and programs transition to routinely vaccinating all children.

· Either TIV or LAIV can be used when vaccinating healthy persons aged 2-49
years. Children aged 6 months-8 years should receive 2 doses of vaccine if they
have not been vaccinated previously at any time with either LAIV or TIV (doses
separated by >4 weeks); 2 doses are required for protection in these children.
Children aged 6 months-8 years who received only 1 dose in their first year of
vaccination should receive 2 doses the following year. LAIV should not be
administered to children aged <5 years with possible reactive airways disease,
such as those who have had recurrent wheezing or a recent wheezing episode.
Children with possible reactive airways disease, persons at higher risk for
influenza complications because of underlying medical conditions, children aged
6-23 months, and persons aged >49 years should receive TIV.

· The 2008--09 trivalent vaccine virus strains are A/Brisbane/59/2007 (H1N1)-like,
A/Brisbane/10/2007 (H3N2)-like, and B/Florida/4/2006-like antigens.
Oseltamivir-resistant influenza A (H1N1) strains have been identified in the
United States and some other countries. However, oseltamivir or zanamivir
continue to be the recommended antivirals for treatment of influenza because
other influenza virus strains remain sensitive to oseltamivir, and resistance levels
to other antiviral medications remain high.


Clinical Signs and Symptoms of Influenza

Influenza viruses are spread from person to person primarily through large-particle
respiratory droplet transmission (e.g., when an infected person coughs or sneezes near a susceptible person). Transmission via large-particle droplets requires close contact between source and recipient persons, because droplets do not remain suspended in the air and generally travel only a short distance (<1 meter) through the air. Contact with respiratory-droplet contaminated surfaces is another possible source of transmission. Airborne transmission (via small-particle residue [<5µm] of evaporated droplets that
might remain suspended in the air for long periods of time) also is thought to be possible, although data supporting airborne transmission are limited. The typical incubation period for influenza is 1--4 days (average: 2 days). Adults shed influenza virus from the day before symptoms begin through 5--10 days after illness onset. However, the amount of virus shed, and presumably infectivity, decreases rapidly by 3--5 days after onset in an experimental human infection model. Young children also might shed virus several days before illness onset, and children can be infectious for >10 days after onset of symptoms.

Severely immunocompromised persons can shed virus for weeks or months. Uncomplicated influenza illness is characterized by the abrupt onset of constitutional and respiratory signs and symptoms (e.g., fever, myalgia, headache, malaise, nonproductive cough, sore throat, and rhinitis). Among children, otitis media, nausea, and vomiting also are commonly reported with influenza illness. Uncomplicated influenza illness typically resolves after 3--7 days for the majority of persons, although cough and malaise can persist for >2 weeks. However, influenza virus infections can cause primary influenza viral pneumonia; exacerbate underlying medical conditions (e.g., pulmonary or cardiac disease); lead to secondary bacterial pneumonia, sinusitis, or otitis media; or contribute to co-infections with other viral or bacterial pathogens. Young children with influenza virus infection might have initial symptoms mimicking bacterial sepsis with high fevers, and
febrile seizures have been reported in 6%--20% of children hospitalized with influenza virus infection. Population-based studies among hospitalized children with laboratory-confirmed influenza have demonstrated that although the majority of hospitalizations are brief (<2 days), 4%--11% of children hospitalized with laboratory-confirmed influenza required treatment in the intensive care unit, and 3% required mechanical ventilation.

Among 1,308 hospitalized children in one study, 80% were aged <5 years, and 27% were aged <6 months. Influenza virus infection also has been uncommonly associated with encephalopathy, transverse myelitis, myositis, myocarditis, pericarditis, and Reye syndrome.

Options for Controlling Influenza

The most effective strategy for preventing influenza is annual vaccination. Strategies that focus on providing routine vaccination to persons at higher risk for influenza complications have long been recommended, although coverage among the majority of these groups remains low. Routine vaccination of certain persons (e.g., children, contacts of persons at risk for influenza complications, and HCP) who serve as a source of influenza virus transmission might provide additional protection to persons at risk for influenza complications and reduce the overall influenza burden, but coverage levels among these persons needs to be increased before effects on transmission can be reliably measured. Antiviral drugs used for chemoprophylaxis or treatment of influenza are adjuncts to vaccine but are not substitutes for annual vaccination. However, antiviral
drugs might be underused among those hospitalized with influenza. Nonpharmacologic interventions (e.g., advising frequent handwashing and improved respiratory hygiene) are reasonable and inexpensive; these strategies have been demonstrated to reduce respiratory diseases but have not been studied adequately to
determine if they reduce transmission of influenza virus. Similarly, few data are available to assess the effects of community-level respiratory disease mitigation strategies (e.g., closing schools, avoiding mass atherings, or using respiratory protection) on reducing influenza virus transmission during typical seasonal influenza epidemics.


Influenza Vaccine Efficacy, Effectiveness, and Safety
Evaluating Influenza Vaccine Efficacy and Effectiveness Studies

The efficacy (i.e., prevention of illness among vaccinated persons in controlled trials) and effectiveness (i.e., prevention of illness in vaccinated populations) of influenza vaccines depend in part on the age and immunocompetence of the vaccine recipient, the degree of similarity between the viruses in the vaccine and those in circulation (see Effectiveness of Influenza Vaccination when Circulating Influenza Virus Strains Differ from Vaccine Strains), and the outcome being measured. Influenza vaccine efficacy and effectiveness studies have used multiple possible outcome measures, including the prevention of medically attended acute respiratory illness (MAARI), prevention of laboratory-confirmed influenza virus illness, prevention of influenza or pneumonia-associated hospitalizations or deaths, or prevention of seroconversion to circulating influenza virus strains. Efficacy or effectiveness for more specific outcomes such as laboratory-confirmed influenza typically will be higher than for less specific outcomes such as MAARI because the causes of MAARI include infections with other pathogens that influenza vaccination would not be expected to prevent. Observational studies that compare less-specific outcomes among vaccinated populations to those among unvaccinated populations are subject to biases that are difficult to control for during analyses. For example, an observational study that determines that influenza vaccination reduces overall mortality might be biased if healthier persons in the study are more likely to be vaccinated. Randomized controlled trials that measure laboratory-confirmed influenza virus infections as the outcome are the most persuasive evidence of vaccine efficacy, but such trials cannot be conducted ethically among groups recommended to receive vaccine annually.


Persons at Risk for Medical Complications

Vaccination to prevent influenza is particularly important for the following persons who are at increased risk for severe complications from influenza, or at higher risk for influenza-associated clinic, emergency department, or hospital visits. When vaccine supply is limited, vaccination efforts should focus on delivering vaccination to these persons:

· all children aged 6 months-4 years (59 months);

· all persons aged >50 years;

· children and adolescents (aged 6 months--18 years) who are receiving long-term aspirin therapy and who might be at risk for experiencing Reye syndrome after influenza virus infection;

· women who will be pregnant during the influenza season;

· adults and children who have chronic pulmonary (including asthma), cardiovascular (except hypertension), renal, hepatic, hematological, or metabolic disorders (including diabetes mellitus);

· adults and children who have immunosuppression (including immunosuppression caused by medications or by HIV);

· adults and children who have any condition (e.g., cognitive dysfunction, spinal cord injuries, seizure disorders, or other neuromuscular disorders) that can compromise respiratory function or the handling of respiratory secretions or that can increase the risk for aspiration;

· residents of nursing homes and other chronic-care facilities.